Your XPath was almost correct. You'll just have to leave out the @ sign. The @ sign is used to indicate that you are trying to check an attribute. To check for element content all you need to to is omit the @:
//Header/reference[Identifier = "BatchProcessed"]
I'm not sure if the double quotes are really needed, but I put them there just the same as I usually write my XPaths that way. Your XPath will fetch you all
Header
tags that have child elements
reference
with sub children
identifier
with a text value of "BatchProcessed".
Best Regards,
—MRB